How to create single JSON for all matching results? - php

Question

I am fetching data from the database, and while I'm fetching, I check for each result if it matches certain criteria, if it does, I want it to add the row with all the details as a new object inside the same JSON, so that I end up with a single JSON that holds all the matching rows
while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
if (matching criteria){
//add row to the JSON
}
}
Right now I can add each row and echo it, but it overwrites the previous row:
while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
if (matching criteria){
$firstColumn = $result['firstColumn'];
$secondColumn= $result['secondColumn'];
//more columns if necessary. . .
$myObj->firstColumn = $firstColumn ;
$myObj->secondColumn= $secondColumn;
$myJSON = json_encode($myObj);
echo $myJSON;
}
}

Answer 1

you can use PDO::fetch_object for ever row and add them to assoc array/another object and then use the json_encode on it.
something like (pseudocode not tested) it will create json array with object for every row:
$out = [];
while($result = $stmt->fetch(PDO::FETCH_OBJ)
{
if(matching){
$out[] = $result;
}
}
echo json_encode($out);

Answer 2

Try this way create a array assign value to that array with myObj Data and after get collection of array convert into Json object
$data = array(array());
$i = 0;
$j = 0;
while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
if (matching criteria){
$firstColumn = $result['firstColumn'];
$secondColumn= $result['secondColumn'];
//more columns if necessary. . .
$myObj->firstColumn = $firstColumn ;
$myObj->secondColumn= $secondColumn;
$data[i][j]=$firstColumn;
$j++;
$data[i][j]=$secondCoulmn;
$i++;
$j--;
}
}
$myJSON = json_encode($data);
echo $myJSON;